This invention relates to mass flow determinations primarily intended for a fuel injection system in spark-ignition engines, but which also has other applications. For the purpose of general description, we shall refer to the invention as being applied to the primary application.
The purpose of any fuel delivery system in a spark ignition engine is to achieve as closely as possible a desired air/fuel mixture regardless of engine and ambient air temperature and atmospheric pressure, such mixture requirements being determined by engine speed and load. In modern fuel injection systems used on spark-ignition engines measured fuel delivery is achieved by varying the opening time of solenoid-operated fuel injectors. This time is calculated by a processor which is often part of the total engine management system which system, in turn, requires various engine parameters to be input to supply the data for such calculations.
Calculation of mass flow of air is an essential part of injection systems and various methods have been employed to achieve this.
These include:
1. Mass airflow direct measurement, whereby air pressure is measured by a mass flow sensing device placed in the air induction passage. With a ratio of at least 40:1 and a possible ratio of 150:1 between maximum and minimum mass airflow, this method makes accuracy at low values of flow difficult to achieve. Despite this and other problems this method remains the favoured means of mass air flow determination in road cars.
2. Speed-density control, an indirect method which uses the fact that an engine behaves as a positive displacement air pump. From engine speed, induction air pressure and temperature, as well as atmospheric pressure, this method allows computation of the air mass flow of the engine. This method requires more complex calculations, but yields more consistent results over the range of mass flows. For most engine types this indirect method provides a good estimate of mass air flow under most conditions of engine operation.
The method, however, copes poorly with engine configurations where the throttle is situated in the air induction system in a position relative to the inlet port such that throttle opening affects the velocity and hence the kinetic energy of the incoming air and/or changes the acoustic resonance of the air contained in the air induction system. In spite of the abovementioned limitation of this method it has been in widespread use on many motor vehicles. It has been the preferred indirect method used with forced induction engines.
3. Speed-throttle method. This is also an indirect method which uses the fact that an engine""s air consumption can be controlled by an intakes throttling device. From engine speed, throttle opening, ambient air temperature and ambient air pressure, this method allows computation of the air mass flow of the engine. This method requires complex calculations, offers limited accuracy during heavy throttling and is incompatible with most of the additional devices added to modern engines for exhaust emission reduction.
Because the function includes a throttle dependant term this method copes well with engine configurations that incorporate induction systems involving throttle-opening dependent kinetic energy changes and throttle-opening dependent induction-system resonance changes. For this reason it is the indirect method of choice for non-forced induction high performance racing engines.
With no induction pressure term in the calculation, this method is incompatible with forced induction engines.
4. A fourth method the xe2x80x9cSpeed-density-throttle methodxe2x80x9d, estimates mass airflow from measurements of engine speed, induction air pressure, induction air temperature, throttle opening and ambient air pressure. This method is compatible with almost all engine types yet is rarely if ever employed, because of the difficulties of implementing a calibration strategy that can evaluate the mathematical function for airmass flow, this latter being primarily dependent upon four variables, engine speed, throttle position, induction air temperature and induction air pressure.
It is an object of the invention to overcome the practical difficulties in this last-named fourth method.
The invention in its broadest sense provides a fuel-injected internal combustion engine with electronic control of air fuel ratio employing a throttle for air flow control, means for sensing pressure downstream of such throttle, means for measuring the speed of the engine and means for measuring the opening of such throttle characterised in that the parameters are fed to a processor and the algorithms used by the processor to compute total intake mass air flow contains the product of two terms, one substantially representing a function of the downstream air pressure, as derived from said sensor, and the other being substantially a function of engine speed and throttle opening as determined by said measuring means.
The invention also includes a method of calculating the mass air flow in a fuel-injected internal combustion engine of the kind providing electronic control of air fuel ratio employing a throttle for air flow control, including sensing pressure downstream of such throttle, measuring the speed of the engine and measuring the opening of such throttle characterised in that the algorithms used to compute total intake mass air flow contains the product of two terms, one substantially representing a function of the downstream air pressure, and the other being substantially a function of engine speed and throttle opening as determined.
In many applications, the pressure function can be very simple and can be a linear function based on the sensor reading. Alternatively, for some engines, it can be a more complex function and, if this is the case, it may be necessary to develop a look-up table based on different pressure values.